The door is left open for Danario Alexander to attract outside suitors in free agency.

A league source confirmed Saturday the Chargers have put the lowest tender on the wide receiver, who is a restricted free agent. The tender gives San Diego the right of first refusal — the ability to match any contract offer Alexander receives — without the chance to receive draft compensation if Alexander ultimately signs elsewhere.

Restricted free agents typically don't create much action.

The chance to throw a hat into the ring of a high-upside receiver like Alexander without losing a draft pick may create an exception.

At age 24, Alexander was the Chargers' most productive offensive player over the second half of last season. He signed in late October during Week 8 and, over the final nine games, had team highs of 37 catches for 658 yards and seven scores. The touchdown catch total tied for third most in the NFL in that span, and the yardage ranked 14th.

In terms of talent, Alexander has the size and skill set to warrant an average annual price tag of several millions of dollars. But his injury history — his left knee has undergone four surgeries — will likely temper a team's investment, and by placing the original tender on Alexander, the Chargers are allowing other teams to set the market while still retaining the right to match it.

Alexander earned slightly more than $300,000 in split salary with the Chargers in 2012.